Download estrogen-only menopausal therapy

ESTROGEN-ONLY MENOPAUSAL THERAPY
Estrogen therapy was considered by previous IARC Working Groups in 1987 and 1998 (IARC,
1987, 1999). Since that time, new data have become available, these have been incorporated into the Monograph, and taken into consideration in the present evaluation.
1. Exposure Data
(i) Structural and molecular formulae, and
molecular mass
1.1 Identification of the agents
CH3
O
1.1.1 Conjugated estrogens
The term ‘conjugated estrogens’ refers to
mixtures of at least eight compounds, including
sodium estrone sulfate and sodium equilin
sulfate, derived wholly or in part from equine
urine or synthetically from estrone and equilin.
Conjugated estrogens contain as concomitant
components the sodium sulfate conjugates of
17α-dihydroequilin, 17β-dihydroequilin, and
17α-estradiol (United States Pharmacopeial
Convention, 2007).
(a) Sodium estrone sulfate
Chem. Abstr. Serv. Reg. No.: 438-67-5
Chem. Abstr. Name: 3-(Sulfooxy)-estra1,3,5(10)-trien-17-one, sodium salt
IUPAC Systematic Name: Sodium
[(8R,9S,13S,14S)-13-methyl-17-oxo7,8,9,11,12,14,15,16-octahydro-6Hcyclopenta[a]phenanthren-3-yl] sulfate
Synonyms: Estrone sodium sulfate; estrone
sulfate sodium; estrone sulfate sodium salt;
oestrone sodium sulfate; oestrone sulfate sodium; oestrone sulfate sodium salt;
sodium estrone sulfate; sodium estrone3-sulfate; sodium oestrone-3-sulfate
H
H
H
N aO 3 SO
C18H21O5S.Na
Relative molecular mass: 372.4
(b) Sodium equilin sulfate
Chem. Abstr. Serv. Reg. No.: 16680-47-0
Chem. Abstr. Name: 3-(Sulfooxy)-estra1,3,5(10),7-tetraen-17-one, sodium salt
IUPAC Systematic Name: Sodium
(13-methyl-17-oxo-9,11,12,14,15,16-hexahydro-6H-cyclopenta[a]phenanthren-3-yl)
sulfate
Synonyms: Equilin, sulfate, sodium salt;
equilin sodium sulfate; sodium equilin
3-monosulfate
Description: buff-coloured amorphous powder, odourless or with a slight characteristic
odour [when obtained from natural sources]; white to light-buff-coloured crystalline
or amorphous powder, odourless or with a
slight odour [synthetic form] (Sweetman,
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IARC MONOGRAPHS – 100A
2008)
1.1.3Mestranol
(i) Structural and molecular formulae, and
molecular mass
CH3
H
O
H
N aO 3 SO
C18H19O5S.Na
Relative molecular mass: 370.4
1.1.2Ethinylestradiol
Chem. Abstr. Serv. Reg. No.: 57-63-6
Chem. Abstr. Name: (17α)-19-Norpregna1,3,5(10)-trien-20-yne-3,17-diol
IUPAC Systematic Name:
(8R,9S,13S,14S,17R)-17-Ethynyl-13-methyl-7,8,9,11,12,14,15,16-octahydro-6Hcyclopenta[a]phenanthrene-3,17-diol
Synonyms: 17-Ethinyl-3,17-estradiol;
17-ethinylestradiol; 17α-ethinyl17β-estradiol; ethinylestradiol;
17α-ethinylestradiol
Description: White to creamy- or slightly
yellowish-white, odourless, crystalline powder (Sweetman, 2008)
(a) Structural and molecular formulae, and
relative molecular mass
CH 3
OH
C
Chem. Abstr. Serv. Reg. No.: 72-33-3
Chem. Abstr. Name: (17α)-3-Methoxy-19norpregna-1,3,5(10)-trien-20-yn-17-ol
IUPAC Systematic Name:
(8R,9S,13S,14S,17R)-17-Ethynyl-3-methoxy-13-methyl-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthren-17-ol
Synonyms: Ethinylestradiol 3-methyl
ether; 17α-ethinylestradiol 3-methyl
ether; ethinyloestradiol 3-methyl ether;
17α-ethinyloestradiol 3-methyl ether;
ethynylestradiol methyl ether; ethynylestradiol 3-methyl ether; 17-ethynylestradiol 3-methyl ether; 17α-ethynylestradiol
3-methyl ether; 17α-ethynylestradiol
methyl ether; ethynyloestradiol methyl ether; ethynyloestradiol 3-methyl
ether; 17-ethynyloestradiol 3-methyl
ether; 17α-ethynyloestradiol 3-methyl
ether; 17α-ethynyloestradiol methyl
ether; 3-methoxy-17α-ethinylestradiol;
3-methoxy-17α-ethinyloestradiol;
3-methoxy-17α-ethynylestradiol; 3-methoxyethynylestradiol; 3-methoxy-17αethynyloestradiol; 3-methoxyethynyloestradiol; 3-methylethynylestradiol;
3-O-methylethynylestradiol; 3-methylethynyloestradiol; 3-O-methylethynyloestradiol;
∆-MVE
Description: White or almost white to
creamy-white, odourless, crystalline powder (Sweetman, 2008)
(a) Structural and molecular formulae, and
relative molecular mass
CH
CH3
OH
C
H
H
H
H
H
HO
C20H24O2
Relative molecular mass: 296.4
220
H
H 3 CO
C21H26O2
Relative molecular mass: 310.4
CH
Estrogen-only menopausal therapy
1.1.4Estradiol
Chem. Abstr. Serv. Reg. No.: 50-28-2
Chem. Abstr. Name: (17β)-Estra-1,3,5(10)triene-3,17-diol
IUPAC Systematic Name:
(8R,9S,13S,14S,17S)-13-Methyl-6,7,8,9,11,12,14,15,16,17decahydrocyclopenta[a]phenanthrene-3,17-diol
Synonyms: Dihydrofollicular hormone;
dihydrofolliculin; dihydromenformon; dihydrotheelin; dihydroxyestrin;
3,17β-dihydroxyestra-1,3,5(10)-triene;
3,17-epidihydroxyestratriene; β-estradiol;
17β-estradiol; 3,17β-estradiol; (d)-3,17βestradiol; oestradiol-17β; 17β-oestradiol
Description: White or creamy-white, odourless, crystalline powder (Sweetman, 2008)
(a) Structural and molecular formulae, and
relative molecular mass
CH 3
OH
H
H
H
17β-estradiol benzoate; 17β-estradiol
3-benzoate; estradiol monobenzoate;
1,3,5(10)-estratriene-3,17β-diol 3-benzoate; β-oestradiol benzoate; β-oestradiol
3 benzoate; 17β-oestradiol benzoate;
17β-oestradiol 3-benzoate; oestradiol
monobenzoate; 1,3,5(10)-oestratriene3,17β-diol 3-benzoate
Description: Almost white crystalline powder or colourless crystal (Sweetman, 2008)
(a) Structural and molecular formulae, and
relative molecular mass
CH3
OH
H
H
O
C
H
H
O
C25H28O3
Relative molecular mass: 376.5
1.1.6 Estradiol cypionate
H
HO
C18H24O2
Relative molecular mass: 272.4
1.1.5 Estradiol benzoate
Chem. Abstr. Serv. Reg. No.: 50-50-0
Chem. Abstr. Name: Estra-1,3,5(10)-triene3,17β-diol, 3-benzoate
IUPAC Systematic Name:
[(8R,9S,13S,14S,17S)-17-Hydroxy13-methyl-6,7,8,9,11,12,14,15,16,17decahydrocyclopenta[a]phenanthren-3-yl]
benzoate
Synonyms: Estradiol benzoate; β-estradiol
benzoate; β-estradiol 3-benzoate;
Chem. Abstr. Serv. Reg. No.: 313-06-4
Chem. Abstr. Name: (17β)-Estra-1,3,5(10)triene-3,17-diol, 17-cyclopentanepropanoate
IUPAC Systematic Name:
[(8R,9S,13S,14S,17S)-3-Hydroxy13-methyl-6,7,8,9,11,12,14,15,16,17decahydrocyclopenta[a]phenanthren-17-yl]
3- cyclopentylpropanoate
Synonyms: Cyclopentanepropionic acid,
17-ester with oestradiol; cyclopentanepropionic acid, 3-hydroxyestra-1,3,5(10)trien-17β-yl ester; depo-estradiol cyclopentylpropionate; depoestradiol cypionate;
estradiol 17β-cyclopentanepropionate;
estradiol cyclopentylpropionate; estradiol 17-cyclopentylpropionate; estradiol
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IARC MONOGRAPHS – 100A
17β-cyclopentylpropionate; 17β-estradiol
17-cyclopentyl-propionate; estradiol cypionate; estradiol 17-cypionate; estradiol
17β-cypionate
Description: White to practically white crystalline powder, odourless or with a slight
odour (Sweetman, 2008)
(a) Structural and molecular formulae, and
relative molecular mass
O
CH 3
O
C
H
H
H
H
HO
C26H36O3
Relative molecular mass: 396.6
1.1.7 Estradiol valerate
Chem. Abstr. Serv. Reg. No.: 979-32-8
Chem. Abstr. Name: (17β)-Estra-1,3,5(10)triene-3,17-diol, 17-pentanoate
IUPAC Systematic Name:
[(8R,9S,13S,14S,17S)-3-Hydroxy13-methyl-6,7,8,9,11,12,14,15,16,17decahydrocyclopenta[a]phenanthren-17-yl]
pentanoate
Synonyms: Oestradiol valerate; estradiol
17β-valerate; estradiol valerianate; estra1,3,5(10)-triene-3,17β-diol 17-valerate;
3-hydroxy-17β-valeroyloxyestra-1,3,5(10)triene
Description: White or almost white crystalline powder or colourless crystal, odourless or with a faint fatty odour (Sweetman,
2008)
(a) Structural and molecular formulae, and
relative molecular mass
O
CH 3
O
C
H
H
H
HO
C23H32O3
Relative molecular mass: 356.5
1.1.8Estriol
Chem. Abstr. Serv. Reg. No.: 50-27-1
Chem. Abstr. Name: (16α,17β)-Estra1,3,5(10)-triene-3,16,17-triol
IUPAC Systematic Name:
(8R,9S,13S,14S,16R,17R)-13-Methyl-6,7,8,9,11,12,14,15,16,17decahydrocyclopenta[a]phenanthrene3,16,17-triol
Synonyms: Estra-1,3,5(10)-triene3,16α,17β-triol; estratriol; 16α-estriol;
16α,17β-estriol; 3,16α,17β-estriol; follicular
hormone hydrate; 16α-hydroxyestradiol;
3,16α,17β-trihydroxyestra-1,3,5(10)-triene;
trihydroxyestrin
Description: White or practically white,
odourless, crystalline powder (Sweetman,
2008)
(a) Structural and molecular formulae and
relative molecular mass
CH 3
OH
H
H
H
OH
H
H
HO
C18H24O3
Relative molecular mass: 288.4
222
CH 3
H
Estrogen-only menopausal therapy
1.1.9Estrone
Chem. Abstr. Serv. Reg. No.: 53-16-7
Chem. Abstr. Name: 3-Hydroxyestra1,3,5(10)-trien-17-one
IUPAC Systematic Name: (8R,9S,13S,14S)3-Hydroxy-13-methyl-7,8,9,11,12,14,15,16octahydro-6H- cyclopenta[a]phenanthren17-one
Synonyms: d-Estrone; d-oestrone
Description: Odourless, small white crystals
or white to creamy-white crystalline powder (Sweetman, 2008)
(a) Structural and molecular formulae, and
relative molecular mass
CH 3
O
H
H
(a) Structural and molecular formulae, and
relative molecular mass
CH 3
O
H
NH2
+
O
HN
-O
S
H
H
O
O
C22H32N2O5S
Relative molecular mass: 436.6
1.2Use of the agents
Information for Section 1.2 is taken from
IARC (1999) and McEvoy (2007).
1.2.1Indications
H
HO
C18H22O2
Relative molecular mass: 270.4
1.1.10Estropipate
Chem. Abstr. Serv. Reg. No.: 7280-37-7
Chem. Abstr. Name: 3-(Sulfooxy)-estra1,3,5(10)-trien-17-one, compd. with piperazine (1:1)
IUPAC Systematic Name: [(8R,9S,13S,14S)13-Methyl-17-oxo-7,8,9,11,12,14,15,16octahydro-6H-cyclopenta[a]phenanthren3-yl] hydrogen sulfate: piperazine (1:1)
Synonyms: Piperazine estrone sulfate;
piperazine oestrone sulfate; 3-sulfatoxyestra-1,3,5(10)-trien-17-one piperazine salt;
3-sulfatoxyoestra-1,3,5(10)-trien-17-one
piperazine salt
Description: White or almost white to
yellowish-white, fine crystalline powder,
odourless or with a slight odour (Sweetman, 2008)
Menopausal estrogen therapy refers to the
use of estrogen without a progestogen for women
in the period around the menopause, primarily
for the treatment of menopausal symptoms
but also for the prevention of conditions that
become more common in the postmenopausal
period, such as osteoporosis and ischaemic heart
disease. It is mainly given to women who have
had a hysterectomy.
Conjugated estrogens, estradiol and its semisynthetic esters (especially estradiol valerate),
are the main estrogens used in the treatment of
menopausal disorders. Their use has also been
proposed in the prevention of cardiovascular
diseases. Conjugated estrogens have been used
extensively in the United Kingdom, Australia,
Canada, and the United States of America for
the treatment of climacteric [menopausal] symptoms. In Europe, micronised estradiol and estradiol valerate are used. Mestranol, estriol, and
estropipate have also been used.
Estrogens may be used adjunctively with other
therapeutic measures (e.g. diet, calcium, vitamin
D, weight-bearing exercise, physical therapy) to
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IARC MONOGRAPHS – 100A
retard bone loss and the progression of osteoporosis in postmenopausal women, either orally
(e.g. estradiol, estropipate, conjugated estrogens)
or transdermally (e.g. estradiol).
Estrogens are also used in the treatment of a
variety of other conditions associated with a deficiency of estrogenic hormones, including female
hypogonadism, castration, and primary ovarian
failure. In addition, estrogens may be used in the
treatment of abnormal uterine bleeding caused
by hormonal imbalance not associated with an
organic pathology.
Oral conjugated estrogens and ‘synthetic
conjugated estrogens A’ [‘synthetic conjugated
estrogens A’ are a mixture of nine derivatives
of estrone, equilin, estradiol, and equilenin] are
used for the management of moderate-to-severe
vasomotor symptoms associated with menopause, and for the management of vulvar and
vaginal atrophy (atrophic vaginitis); for the latter,
topical vaginal preparations are used.
‘Synthetic conjugated estrogens B’ [a mixture
of ten derivatives of estrone, equilin, estradiol,
and equilenin] are used for the management of
moderate-to-severe vasomotor symptoms associated with menopause. Oral conjugated estrogens are also used for the management of female
hypoestrogenism secondary to hypogonadism,
castration, or primary ovarian failure.
Estradiol is the most active of the naturally
occurring estrogens. Estradiol and its semisynthetic esters are used primarily as menopausal
therapy. Estradiol may also be used for female
hypogonadism or primary ovarian failure.
Although ethinylestradiol is used most
extensively in oral contraceptives in combination with a progestogen, other indications
include perimenopausal symptoms, hormonal
therapy for hypogonadal women, treatment of
postpartum breast engorgement, dysfunctional
uterine bleeding, and therapy for carcinoma of
the breast and prostate.
224
1.2.2Dosages and preparations
Menopausal estrogen therapy is administered in a continuous daily dosage regimen or,
alternatively, in a cyclic regimen. When estrogens are administered cyclically, the drugs are
usually given once daily for 3 weeks followed
by a 1 week washout period, or once daily for
25 days followed by 5 days washout, repeated as
necessary.
Menopausal estrogen therapy is available
as oral tablets, intranasal sprays, subcutaneous
implants, topical applications for vulvovaginal
use, intravaginal rings, and transdermal skin
patches and gels.
(a) Conjugated estrogens
For the treatment of climacteric symptoms,
conjugated estrogens are usually administered
orally in a dose of 0.3–1.25 mg daily. Conjugated
estrogens may also be administered intravaginally or by deep intramuscular or slow intravenous injection. When parenteral administration
of conjugated estrogens is required, slow intravenous injection is preferred because of the more
rapid response obtained following this route
of administration compared to intramuscular
injection. Topical vaginal therapy may be used
specifically for menopausal atrophic vaginitis:
0.5–2 g of a 0.0625% cream may be used daily for
3 weeks of a 4-week cycle.
For the management of moderate-to-severe
vasomotor symptoms associated with menopause, the usual oral dosage of ‘synthetic conjugated estrogens A’ is 0.45–1.25 mg daily, usually
starting with 0.45 mg daily, and with any
subsequent dosage adjustments dependent on
the patient’s response. For the management of
vulvar and vaginal atrophy, the usual oral dosage
of ‘synthetic conjugated estrogens A’ is 0.3 mg
daily. The usual initial oral dosage of ‘synthetic
conjugated estrogens B’ for the management of
moderate-to-severe vasomotor symptoms associated with menopause is 0.3 mg daily, with any
Estrogen-only menopausal therapy
subsequent dosage adjustment dependent on the
patient’s response.
For the prevention of osteoporosis, the usual
initial oral dosage of conjugated estrogens is
0.3 mg once daily. Subsequent dosage should be
adjusted based on the patient’s clinical and bone
mineral density responses. The drug may be
administered in a continuous daily regimen or
in a cyclic regimen (25 days on drug, followed by
a 5-day washout period, repeated as necessary).
For therapy in female hypoestrogenism, the
usual oral dosage of conjugated estrogens is
0.3–0.625 mg daily in a cyclic regimen (3 weeks
on drug, followed by a 1-week washout period).
For the management of female castration or
primary ovarian failure, the usual initial oral
dosage of conjugated estrogens is 1.25 mg daily
in a cyclic regimen.
For the palliative treatment of prostatic carcinoma, an oral dose of 1.25–2.5 mg conjugated
estrogens three times daily has been used. A dose
of 10 mg three times daily for at least 3 months
has been used for the palliative treatment of
breast carcinoma in men and in postmenopausal
women. Abnormal uterine bleeding has been
treated acutely by giving 25 mg of conjugated
estrogens by slow intravenous injection, repeated
after 6–12 hours if required; the intramuscular
route has also been used.
(b) Single estrogens
Ethinylestradiol has been used for menopausal therapy at doses of 10–20 µg daily.
Mestranol is rapidly metabolized to ethinylestradiol, therefore, acts in a similar fashion
to that of estradiol. It has been used as the
estrogen component of some preparations for
menopausal therapy. It was usually given in a
sequential regimen with doses ranging from
12.5–50 µg daily.
Estradiol may be used topically as transdermal
skin patches that release between 14–100 µg of
estradiol every 24 hours to provide a systemic
effect. A low-dose patch supplying 14 µg daily
is also available. Topical gel preparations can
be applied to also provide a systemic effect;
the usual dose is 0.5–1.5 mg of estradiol daily.
A topical emulsion of estradiol is also available
as the hemihydrate with a daily dose of 8.7 mg.
This is also available as a nasal spray, delivering
150 µg of estradiol hemihydrate per spray. The
usual initial dose is 150 µg daily. After two or
three cycles the dose may be adjusted according
to the response; the usual maintenance dose is
300 µg daily but may range from 150 µg once
daily up to 450–600 µg daily in two divided
doses.
Subcutaneous implants of estradiol may also
be used in doses of 25–100 mg with a new implant
being given after about 4–8 months, depending
on whether therapeutic concentrations of estrogens are detected in the plasma.
Estradiol may be used locally either as
25 µg vaginal tablets, at an initial dose of one
tablet daily for 2 weeks, followed by a maintenance dose of one tablet twice a week, or as a
0.01% vaginal cream in initial amounts of 2–4 g
of cream daily for 1–2 weeks followed by half the
initial dose for a similar period, then a maintenance dose of 1 g up to three times weekly. Also
available for the relief of both local and systemic
postmenopausal symptoms are local delivery
systems using 3-month vaginal rings containing
2 mg of estradiol hemihydrate that release about
7.5 µg of estradiol daily or estradiol acetate that
release either 50 or 100 µg of estradiol daily.
Intramuscular injections of estradiol benzoate
or valerate esters have been used as oily depot
solutions, given once every 3–4 weeks. The cypionate, dipropionate, enantate, hexahydrobenzoate, phenylpropionate, and undecylate esters
have been used similarly. The enantate and cypionate esters are used as the estrogen component
of combined injectable contraceptives (estradiol
and other estrogens have sometimes been used at
higher doses for the palliative treatment of prostate cancer and breast cancer in men, and breast
cancer in postmenopausal women.)
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IARC MONOGRAPHS – 100A
Estriol is a naturally occurring estrogen
with actions and uses that are similar to those
described for estradiol valerate. For short-term
treatment, oral doses of estriol are 0.5–3 mg
daily given for 1 month, followed by 0.5–1 mg
daily. Estriol has also been given with other
natural estrogens, such as estradiol and estrone,
with usual doses of estriol ranging from about
0.25–2 mg daily. Estriol is given intravaginally
for the short-term treatment of menopausal
atrophic vaginitis as a 0.01% or 0.1% cream or
as pessaries containing 500 µg. It has also been
given orally for infertility in doses of 0.25–1 mg
daily on Days 6 to 15 of the menstrual cycle.
Estriol succinate has also been given orally for
menopausal disorders. The sodium succinate salt
has been used parenterally in the treatment of
haemorrhage and thrombocytopenia.
Estrone has been given in oral doses of
1.4–2.8 mg daily in a cyclic or continuous
regimen for menopausal symptoms, and as a
combination product with estradiol and estriol.
Estrone has also been given by intramuscular
injection in formulations with oily solutions
or aqueous suspensions. When used for menopausal atrophic vaginitis, estrone has been given
vaginally.
Estropipate is used for the short-term treatment of menopausal symptoms; suggested doses
range from 0.75–3 mg daily, given cyclically or
continuously orally; doses of up to 6 mg daily have
also been given cyclically. When used long-term
for the prevention of postmenopausal osteoporosis, a daily dose of 0.75–1.5 mg is given cyclically
or continuously. Estropipate has also been used
short-term for menopausal atrophic vaginitis as
a 0.15% vaginal cream; 2–4 g of cream is applied
daily. It can be given orally in the treatment of
female hypogonadism, castration, and primary
ovarian failure in doses of 1.5–3 mg daily, in a
cyclic regimen; higher doses of up to 9 mg daily
given cyclically have also been used.
226
1.2.3Formulations
Conjugated estrogens are available as
0.3–1.25 mg tablets for oral administration, as
a 25 mg solution for parenteral administration,
and as a 0.0625% cream for topical administration. Synthetic conjugated estrogens A and B are
available as 0.3–1.25 mg film-coated tablets for
oral administration. Estradiol (alone) is available as a 0.06% gel and as a transdermal patch
with doses ranging from 14–100 μg/24 hours for
topical administration, as a 0.01% cream, and as
a 2 mg/ring for vaginal administration. Estradiol
(hemihydrate) is available as a 0.25% emulsion for
topical administration and as 25 µg (of estradiol)
film-coated tablets for vaginal administration.
Estradiol (micronized) is available as 0.5–2 mg
tablets for oral administration. Estradiol acetate is
available as 0.45–1.8 mg tablets for oral administration, and as a 12.4–24.8 mg/ring (0.05–0.1 mg
estradiol/24 hours) for vaginal administration.
Estradiol cypionate is available as a 5 mg/mL
injection solution in oil for parenteral administration. Estradiol valerate is available as a
10–40 mg/mL injection solution in oil for parenteral administration. Estropipate is available as
0.75–3 mg tablets for oral administration.
1.2.4 Trends in use
Early treatment regimens of menopausal
symptoms included estrogen-only therapy. After
a substantial increase in use in the 1960s and
early 1970s, the use of these regimens declined
after 1975 when a strong association with the
development of endometrial cancer was found.
Estrogen-only menopausal treatment is still
prescribed for hysterectomized women.
Estrogen-only menopausal therapy
2. Cancer in Humans
Studies were included in this review if they
provided information regarding estrogen use
(unopposed/alone).
2.1Cancer of the breast
The previous IARC Monograph (IARC, 1999)
on postmenopausal estrogen therapy and breast
cancer considered the pooled analysis of original
data from 51 studies, and also reviewed data
from 15 cohort and 23 case–control studies. The
majority of studies showed a small increased risk
in current users who had been using estrogen for
at least 5 years. Several of the studies reviewed
included any hormone therapy and were not
restricted to estrogen alone. Data were insufficient to determine whether the risk varied with
type or dose of estrogen.
The present review of postmenopausal
estrogen therapy taken without a progestogen
(unopposed estrogen) and breast cancer includes
papers published from 1996 to August 2008. It
includes one systematic review, over 20 cohort
and case–control studies combined, and one
randomized trial. Studies were included if they
reported estimated relative risks (RRs), hazard
ratios (HRs) or odds ratios (ORs) and 95%
confidence intervals (CI), and if they compared
women who used unopposed estrogen for at least
1 year with women who used no estrogen.
2.1.1 Systematic review
Greiser et al. (2005) conducted a meta-analysis
of unopposed estrogen therapy and breast cancer
in postmenopausal women, which included 12
case–control studies, five cohort studies, and
three clinical trials published in 1989–2004.
The summary relative risk for studies
published before 1992 showed no increased
breast cancer risk for case–control studies (OR,
1.02; 95%CI: 0.93–1.11). The summary estimate
for case–control studies published later (OR,
1.18; 95%CI: 1.08–1.30) was similar to that
of cohort studies published earlier (OR, 1.19;
95%CI: 1.10–1.28). The summary risks from
cohort studies published in 1992 or later were
largely driven by the Million Women Study
results (OR, 1.30), which showed increased risks
only in current hormone users.
2.1.2 Cohort studies
Of the ten cohort studies reported since 1999,
four found increased risk of breast cancer from
ever use of estrogen alone (Colditz & Rosner,
2000; Beral et al., 2003; Bakken et al., 2004;
Ewertz et al., 2005). The largest published cohort
study is the United Kingdom Million Women
Study (Beral et al., 2003) that included 1084110
women aged 50–64, which found increased risk
of breast cancer by duration of use, and type
of preparation used (see Table 2.1 available at
http://monographs.iarc.fr/ENG/Monographs/
vol100A/100A-12-Table2.1.pdf). The increased
risk was already evident for women with less
than 5 years’ estrogen therapy (OR, 1.21; 95%CI:
1.07–1.37). Several other cohort studies found
increased risks of breast cancer with longer durations of use of estrogen-alone postmenopausal
therapy: Schairer et al. (2000) from 1–2 years
of use but not longer, Olsson et al. (2003) from
48 months or more of use of estriol, Lee et al.
(2006) from 5 or more years of current use (with
a dose–response relationship), and Rosenberg et
al. (2008) from 10 or more years of use in those
with a body mass index (BMI) of less than 25. In
two of the cohort studies, there was no evidence
of an increased risk of breast cancer from
estrogen-alone postmenopausal therapy (Porch
et al., 2002; Fournier et al., 2005).
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2.1.3 Case–control studies
Of the 16 case–control studies, two studies
found increased risk of breast cancer for ever
use of estrogen-alone postmenopausal therapy
(Newcomb et al., 2002; Rosenberg et al., 2008).
In the study of Newcomb et al. (2002), the risk
increase was restricted to those with 5 or more
years of estrogen-alone menopausal therapy, and
in current users with use within the previous
5 years. Some studies found increased risks only
in subgroups: one for those diagnosed with invasive breast cancer (Henrich et al., 1998), one for
users of estrogen-alone postmenopausal therapy
for 60 months or more (principally in those
diagnosed with a lobular breast cancer) (Chen
et al., 2002), one in those who weighed 61.3 kg
or more (Wu et al., 2007), one in those with an
in-situ breast cancer after 5 or more years of use
of estrogen-alone postmenopausal therapy (Ross
et al., 2000), and one in those diagnosed with
comedo carcinomas (Li et al., 2006). Increased
risks in those diagnosed with lobular cancer of
the breast was not confirmed in the studies of
Daling et al. (2002), Li et al. (2002), nor in that
of Li et al. (2003). Kirsh & Kreiger (2002) found
borderline increased risks for those with a duration of use of estrogen alone of 10 or more years,
while Weiss et al. (2002) and Sprague et al. (2008)
found no increases in risk.
See Table 2.2 available at http://
mono g r aph s . i a rc . f r/ E NG/ Mono g r aph s /
vol100A/100A-12-Table2.2.pdf.
2.1.4 Clinical trials
The Women’s Health Initiative estrogen only
trial (WHI-ET) is the only large clinical trial of
unopposed estrogen use (Anderson et al., 2004).
Women were required to have an annual mammogram to receive study medication (see Table 2.3
available at http://monographs.iarc.fr/ENG/
Monographs/vol100A/100A-12-Table2.3.pdf).
At baseline, almost half of the subjects reported
228
prior postmenopausal hormone therapy before
randomization. The trial was closed after an
average 6.8 years follow-up, at which point 218
incident cases of invasive breast cancer were
identified. There was no evidence that oral conjugated equine estrogen (0.625 mg daily) increased
the risk of breast cancer. [The Working Group
noted that the number of women who continued
taking their assigned medication was low, which
could have weakened any effects of estrogen.]
2.2Cancer of the endometrium
The previous IARC Monograph summarized data from hree cohort studies and over 30
case–control studies. These consistently showed
an increased risk of endometrial cancer in women
who received menopausal estrogen therapy. Risk
increased with duration of use, and decreased
with time since last use, but the risk remained
elevated for at least 10 years after cessation of
treatment.
2.2.1 Cohort studies
Results from four cohort studies reported
since the previous IARC Monograph are summarized in Table 2.4 (available at http://monographs.
iarc.fr/ENG/Monographs/vol100A/100A-12Table2.4.pdf), and each found an increased risk
of endometrial cancer from the use of unopposed
estrogen therapy. In the Million Women Study
(Beral et al., 2005), the risk was somewhat lower
in women with a BMI of < 25 kg/m2 than in
women with a BMI of 25 kg/m2 or more. In two
of the cohort studies (Lacey et al., 2005, 2007),
the risk of endometrial cancer increased with
duration of use, and decreased with time since
last use. The risk remained elevated over that of
non-users after 5 or more years since cessation
of use in one study (Lacey et al., 2007), and 10 or
more in the other (Lacey et al., 2005).
Estrogen-only menopausal therapy
2.2.2Case–control studies
2.3Cancer of the colorectum
Results from five case–control studies
reported since the previous IARC Monograph
are summarized in Table 2.5 (available at
http://monographs.iarc.fr/ENG/Monographs/
vol100A/100A-12-Table2.5.pdf), and each found
an increased risk of endometrial cancer in users
of unopposed estrogen of 6 months or more, with
risks increasing with duration of use. In one study
(Shields et al., 1999) that reported additional analyses of data from a prior study, the trend in risk
was observed in women with and without other
risk factors for endometrial cancer (low parity,
hypertension, and BMI), and in women with and
without protective factors (oral contraceptive use
and history of smoking). A total of 85% of the
estrogen users reported using conjugated estrogens. In a population-based study in Sweden
(Weiderpass et al., 1999), the primary estrogen
in use was estradiol. This study also included
women with atypical endometrial hyperplasia.
Risk of this condition was also increased in
estrogen users, and the risk increased with duration of use. In a third study (Beard et al., 2000),
the risk of endometrial cancer was increased
for users of both conjugated estrogens and nonconjugated steroidal estrogens. [The Working
Group noted that steroidal estrogens were not
further defined in the published report.] In one
study (Weiss et al., 2006), the aggressiveness of
endometrial cancers that had been the subject
of a series of population-based cased–control
studies was categorized, based on both tumour
grade and extent of disease. The risk of tumours
of all three levels of aggressiveness increased
with duration of use of estrogen for menopausal
therapy. The increase in risk was greatest for the
cancers with low tumour aggressiveness.
In the previous IARC Monograph (IARC,
1999), 12 case–control and seven cohort studies
provided information on the use of estrogen
therapy and the risk of colorectal cancer. The risk
was not increased and appeared to be reduced
in half of the studies, though the reduced risk
was observed among recent users, and was not
related to duration of use.
2.3.1 Case–control studies
Results from the two case–control studies
reported since the previous IARC Monograph
are summarized in Table 2.6 (available at
http://monographs.iarc.fr/ENG/Monographs/
vol100A/100A-12-Table2.6.pdf). In one study,
no association with colon cancer was found
following recent use of estrogen therapy for a
5- or 10-year period (Jacobs et al., 1999). In the
second study, the odds ratio of colon cancer for
women who had estrogen therapy alone was 0.5
(95%CI: 0.2–0.9) both for those who had used
estrogen within the last year, and for those who
had used estrogen for 5 or more years (Prihartono
et al., 2000).
2.4Cancer of the ovary
In the previous IARC Monograph (IARC,
1999), 12 case–control and four cohort studies
that addressed the risk for ovarian cancer
were considered. No clear association between
estrogen therapy and the risk of ovarian cancer
was found. Since then, there have been seven
case–control and seven cohort studies investigating estrogen-alone exposure and the risk
of ovarian cancer (see Table 2.7 available at
http://monographs.iarc.fr/ENG/Monographs/
vol100A/100A-12-Table2.7.pdf and Table 2.8 at
http://monographs.iarc.fr/ENG/Monographs/
vol100A/100A-12-Table2.8.pdf).
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IARC MONOGRAPHS – 100A
In five of the case–control studies, an increased
risk of ovarian cancer was found with estrogen
alone, though in one, this was only significant for
5 or more years of use (Rossing et al., 2007), and in
two after 10 or more years of use of estrogen for all
types of ovarian cancer combined (Riman et al.,
2002; Moorman et al., 2005). Of the remaining
two case–control studies, one study (Pike et al.,
2004) found a relative risk for 5 years of use of
1.16 (95%CI: 0.92–1.48), and the other did not
find an overall elevation in risk for unopposed
estrogen use for 5 or more years (Sit et al., 2002).
In the three case–control studies that evaluated
risks for different histological types of ovarian
cancer, the findings were not consistent. Thus,
there was a suggestion that risk was elevated for
the endometroid type of ovarian cancer and for
all types of ovarian cancer in women who had
not had a hysterectomy or tubal ligation in one
study (Purdie et al., 1999); in the study in Sweden,
risk was increased for serous type borderline
ovarian cancer (Riman et al., 2001) and for invasive mucinous epithelial ovarian cancer (Riman
et al., 2002), while in the study in the USA, risk
was increased only for serous epithelial cancer
(Moorman et al., 2005), but the numbers were
often very small for the different types. In one
of the case–control studies (Rossing et al., 2007),
the risk among those women who had ceased
estrogen use 3 of more years ago was also evaluated. No increases in risk of ovarian cancer were
found, even among those who had taken estrogen
for 5 or more years (see Table 2.7 online).
In one of the cohort studies, there were only
two cases of ovarian cancer, and the relative risk
was not elevated (Bakken et al., 2004). In the
remaining six cohort studies, the effect of duration of exposure was evaluated (see Table 2.8
online). In one study (Rodriguez et al., 2001), an
elevated risk of death from ovarian cancer was
seen after 10 years of use of estrogen, in another
for incident cases after 10 years of use (Lacey
et al., 2006), in the other four (of incident cases),
after 5 years of use (Lacey et al., 2002; Folsom
230
et al., 2004; Beral et al., 2007; Danforth et al.,
2007). In the study of Lacey et al. (2002), risk
was documented as continuing to increase with
increasing duration of use, the maximum after
20 or more years (RR, 3.4; 95%CI: 1.6–7.5, based
on 14 cases). In another (Rodriguez et al., 2001),
risk of death from ovarian cancer did not seem
to further increase after 5 years of use of estrogen
therapy. In the one cohort study that reported
risk by histological type, risk was significantly
increased for the serous type and the mixed/
other/not-otherwise-specified grouping (Beral
et al., 2007).
In a meta-analysis that included data from
13 case–control studies, three cohort studies
and the WHI-ET trial, the relative risks for ever
use were 1.28 (95%CI: 1.18–1.40), and per year
of estrogen therapy, 1.07 (95%CI: 1.06–1.08)
(Greiser et al., 2007). In another meta-analysis
of 13 population-based case–control and cohort
studies, but not the WHI-ET trial data, [The
Working Group noted that these studies include
three recent studies not included in the Greiser
et al. (2007) meta-analysis] the relative risk per
5 years of use of estrogen use was 1.22 (95%CI:
1.18–1.27) (Pearce et al., 2009). In an additional
meta-analysis, reviewing essentially the same
data, Zhou et al. (2008) computed odds ratios
from the case–control studies of 1.19 (95%CI:
1.01–1.40), and 1.51 (95%CI: 1.21–1.88) from the
cohort studies for ovarian cancer from ever use
of estrogen therapy alone.
2.5Cancer of the urinary bladder
Since the previous IARC Monograph (IARC,
1999), three cohort studies from the USA provide
data on cancer of the urinary bladder in users of
estrogen therapy (Cantwell. et al., 2006; McGrath
et al., 2006; Prizment et al. 2007; see Table 2.9
available at http://monographs.iarc.fr/ENG/
Monographs/vol100A/100A-12-Table2.9.pdf ).
No associations were found between the use of
estrogen therapy and the risk of bladder cancer.
Estrogen-only menopausal therapy
Risk by trend of duration of use was only reported
in one study, and there was no trend in risk with
increasing duration of use.
2.6Cancer of the pancreas
A cohort of 387981 postmenopausal women
in the USA, the Cancer Prevention Study (CPS)-II
(Teras et al., 2005), found no significant positive
trends in pancreatic cancer mortality rates with
years of estrogen therapy use, both for current
and former users.
2.7Exogenous estrogen use and
melanoma risk
A review of the published literature, including
a pooled analysis, concluded that neither oral
contraceptives nor hormone therapy are associated with melanoma risk (Lens & Bataille, 2008).
Two previous pooled analyses, based on 18 and
10 case–control studies, showed summary odds
ratios of 2.0 (95%CI: 1.2–3.4) and 0.86 (95%CI:
0.74–1.01), respectively (Feskanich et al., 1999;
Karagas et al., 2002).
2.8Cancer of the cervix
Only two cohort studies and one case–control
study investigated the relationship between the
use of post-menopausal estrogen therapy and
the risk for invasive cervical cancer. On balance,
the limited evidence available suggests that
postmenopausal estrogen therapy is not associated with an increased risk for invasive cervical
carcinoma. The results provide some suggestion
that postmenopausal estrogen therapy is associated with a reduced risk for cervical cancer, but
the finding could be due to more active screening
for pre-invasive disease among women who
have received postmenopausal estrogen therapy
(IARC, 1999).
2.9Cancer of the thyroid
Seven case–control studies reporting on
thyroid cancer and use of postmenopausal
estrogen therapy did not show an effect on risk
(IARC, 1999).
2.10Synthesis
Estrogen-only menopausal therapy causes
cancer of the endometrium, and of the ovary.
Also, a positive association was observed between
exposure to estrogen-only menopausal therapy
and cancer of the breast. The Working Group also
noted that an inverse relationship is established
between exposure to estrogen-only menopausal
therapy and cancer of the colorectum.
In addition, for cancer of the endometrium,
the risk is increased in users of exogenous
estrogen, and increases with duration of use.
The excess in risk declines with time after use,
but persists for over 10 years after exposure. The
risk is also increased for atypical endometrial
hyperplasia, a presumed precursor of endometrial cancer.
In addition, for cancer of the breast, a
minority of case–control studies show an association between ever use or current use of estrogen
therapy and breast cancer risk. Although the
evidence is less consistent with regard to duration of estrogen therapy use, a few studies point
to an increased risk of breast cancer with longer
term use. The evidence is also inconsistent for
the possibility that estrogen therapy increases
the risk of lobular breast carcinoma. Although at
the time of writing the evidence remains scant,
estrogen therapy does not appear to be related
differently to in-situ versus invasive breast cancer,
to tumour stage, or to hormone receptor status.
The Working Group also concluded that
the use of estrogen-only menopausal therapy is
unlikely to alter the risk of cancer of the thyroid,
bladder, pancreas, cervix, and of melanoma.
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3. Cancer in Experimental Animals
3.1 Summary of the previous IARC
Monograph
3.1.1 Conjugated estrogens
(a) Subcutaneous implantation
(i)Hamster
Hydrolysed conjugated equine estrogens,
equilin and d-equilenin were tested in male
hamsters by subcutaneous implantation. The
hydrolysed estrogens and equilin induced microscopic renal carcinomas, whereas d-equilenin
was inactive (Li et al., 1983).
3.1.2Estradiol
Estradiol and its esters were tested in neonatal
mice, mice, rats, hamsters, guinea-pigs, and
monkeys by subcutaneous injection or implantation, and in mice by oral administration.
(a) Subcutaneous injection or implantation
(i)Mouse
Subcutaneous injections of estradiol to
neonatal mice resulted in precancerous and
cancerous cervical and vaginal lesions in later
life, and an increased incidence of mammary
tumours. Its subcutaneous administration
to mice resulted in increased incidences of
mammary, pituitary, uterine, cervical, vaginal
and lymphoid tumours, and interstitial cell
tumours of the testis (IARC, 1999).
(ii)Rat
Invasive pituitary tumours were induced in
rats treated subcutaneously with estradiol dipropionate (Satoh et al., 1997).
(iii)Hamster
In hamsters, a high incidence of malignant
kidney tumours occurred in intact and castrated
males, and in ovariectomized females treated
232
with estradiol, but not in intact females (Li et al.,
1983; Goldfarb & Pugh, 1990).
The 4-hydroxy metabolite of estradiol induced
renal cell carcinomas in castrated male hamsters
(Liehr et al. 1986; Li & Li, 1987).
(iv)Guinea-pig
In guinea-pigs, diffuse fibromyomatous
uterine and abdominal lesions were observed
(Lipschutz & Vargas, 1941).
(b) Oral administration
(i)Mouse
Oral administration of estradiol to mice
bearing the murine mammary tumour virus
increased the incidences of uterine (endometrial
and cervical) adenocarcinomas and mammary
tumours (Highman et al., 1980).
(c) Administration with known carcinogens
Estradiol was tested in two-stage carcinogenesis models in mice with the known carcinogens
N-methyl-N-nitrosourea (MNU), N-ethyl-Nnitrosourea or 3-methylcholanthrene, and in twostage carcinogenesis models in rats with MNU,
2-acetylaminofluorene, N-nitrosodiethylamine,
7,12-dimethylbenz[a]anthracene (DMBA) or
N-butyl-N-nitrosourea.
(i)Mouse
In mice, estradiol enhanced the incidences of
endometrial adenomatous hyperplasia, atypical
hyperplasia and adenocarcinomas induced by
MNU and N-ethyl-N-nitrosourea (Niwa et al.
1991, 1996). A continuously high serum concentration of estradiol and a low concentration of
progesterone appeared to be important for the
development of endometrial adenocarcinomas in
mice (Takahashi et al., 1996). Estradiol decreased
the development of uterine cervical carcinomas
induced by 3-methylcholanthrene (Das et al.,
1988).
Estrogen-only menopausal therapy
(ii)Rat
In rats, large doses of estradiol alone or estradiol with progesterone suppressed the development of mammary carcinomas induced by MNU
(Grubbs et al., 1983). Combined treatment of
ovariectomized rats with estradiol and MNU
induced vaginal polyps (Sheehan et al., 1982). In
a two-stage model of liver carcinogenesis in rats,
estradiol showed no initiating activity (Sumi et al.,
1984). It did not show promoting effects in the
liver of rats initiated with N-nitrosodiethylamine
(Yager et al., 1984). In one study, pretreatment
with estradiol increased the number of liver
foci positive for γ-glutamyl transferase induced
by N-nitrosodiethylamine (Wotiz et al., 1984).
Estradiol did not affect mammary tumour
development in intact or ovariectomized female
rats treated with DMBA. Estradiol benzoate
enhanced the incidence of mammary tumours
in rats treated with γ-rays (Inano et al., 1995).
3.1.3Estriol
(a) Subcutaneous implantation
(i)Mouse
In castrated mice, estriol increased the
incidence and accelerated the appearance of
mammary tumours in both male and female
mice (Rudali et al., 1975).
(ii)Hamster
In hamsters, estriol produced kidney tumours
(Kirkman, 1959a).
(b) Administration with known carcinogens
(i)Mouse
In female mice, estriol slightly increased the
incidence of MNU-induced endometrial adenocarcinomas (Niwa et al., 1993).
(ii)Rat
In several studies in female rats, estriol inhibited the induction of mammary tumours by
DMBA when administered before the carcinogen;
continuous treatment with estriol resulted in
a decreased incidence of mammary tumours
(Wotiz et al., 1984). In one study in female rats,
estriol inhibited the induction of mammary
carcinomas when administered 13–15 days after
irradiation with γ-rays (Lemon et al., 1989).
3.1.4Estrone
(a) Oral administration
(i)Mouse
Estrone was tested for carcinogenicity by oral
administration in one study in castrated male
mice. The incidence of mammary tumours was
increased (Rudali et al., 1978).
(b) Subcutaneous and/or intramuscular
administration
(i)Mouse
Mammary tumours were induced in male
mice, and the average age at the time of appearance of mammary tumours in female mice was
reduced (Shimkin & Grady, 1940). In two studies
of subcutaneous or intramuscular administration, estrone benzoate induced mammary
tumours in male mice (Bonser, 1936; Shimkin &
Grady, 1940).
(ii)Rat
In castrated male and female rats, subcutaneous injection of estrone resulted in mammary
tumours (Geschickter & Byrnes, 1942). In one
study in rats, subcutaneous injection of estrone
benzoate induced mammary and pituitary
tumours in animals of each sex (Chamorro,
1943).
(c) Subcutaneous implantation
(i)Mouse
In several studies involving subcutaneous
implantation of estrone, the incidences of
mammary and lymphoid tumours were increased
in mice (Bittner, 1941; Gardner & Dougherty,
1944).
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IARC MONOGRAPHS – 100A
(ii)Hamster
In intact and castrated male hamsters,
implantation of estrone resulted in malignant
kidney tumours (Kirkman, 1959b). The estrone
metabolite, 4-hydroxyestrone, induced renal
tumours at a low incidence in castrated male
hamsters (Li & Li, 1987).
(d) Administration with known carcinogens
(i)Mouse
The incidence of endometrial adenocarcinomas induced by MNU in the uterine corpus
of mice was significantly increased in those
receiving an estrone-containing diet; furthermore, the incidences of pre-neoplastic endometrial lesions in the MNU-treated and untreated
uterine corpora were significantly increased in
mice receiving the estrone-containing diet (Niwa
et al., 1993).
(ii)Toad
In one study in female toads, subcutaneous
administration of estrone enhanced the incidence
of hepatocellular carcinomas induced by subcutaneous injection of N-nitrosodimethylamine
(Sakr et al., 1989).
3.2Studies published since the
previous IARC Monograph
See Table 3.1
3.2.1Estradiol
(a)Rat
In a study the objective of which was to characterize some of the genetic bases of estrogeninduced tumorigenesis in the rat, Schaffer et al.
(2006) used young adult female ACI, BN, (BN
x ACI)F1 (F1), and (BN x ACI)F2 (F2) rats that
were treated with estradiol. Whereas nearly 100%
of the ACI rats developed mammary cancer
when treated continuously with estradiol, BN
234
rats did not develop palpable mammary cancer
during the 196-day course of estradiol treatment.
Susceptibility to estradiol-induced mammary
cancer segregated as a dominant or incompletely
dominant trait in a cross between BN females
and ACI males.
3.2.2Administration with known carcinogens
or other modifying agents
(a)Rat
Ting et al. (2007) used three mammary
cancer carcinogen models. DMBA, MNU and
estradiol were combined with local ovarian
DMBA administration to induce progression
to mammary and ovarian cancer concurrently
in rats. Mammary hyperplasia was observed
in DMBA/DMBA- (mammary carcinogen/
ovarian carcinogen) and MNU/DMBA-treated
rats; however, ovarian pre-neoplastic changes
were seldom observed after these treatments.
All estradiol/DMBA-treated rats had mammary
hyperplasia, atypia, ductal carcinoma in situ
and/or invasive adenocarcinoma, and half also
developed pre-neoplastic changes in the ovary
(ovarian epithelial and stromal hyperplasia and
inclusion cyst formation).
Aiyer et al. (2008) fed female ACI rats with
either AIN-93M standard diet or diets supplemented with either powdered blueberry or black
raspberry or ellagic acid. They received estradiol implants and were killed after 24 weeks. A
high incidence of mammary carcinomas was
observed in the AIN-93M group. No differences
were found in tumour incidence at 24 weeks;
however, tumour volume and multiplicity were
reduced significantly in the ellagic acid and black
raspberry groups. The blueberry group showed a
reduction (40%) only in tumour volume.
Callejo et al. (2005) evaluated the influence of
different hormonal environments on the induction of breast cancer in the DMBA-induced
mammary cancer model in rats. Breast cancer
was induced by using a single intragastric dose
Table 3.1 Studies of cancer in experimental animals exposed to estradiol with known carcinogens or other
modifying agents
Species, strain (sex)
Reference
Rat, Female F344 (F)
Ting et al. (2007)
Rat, ACI (F)
Aiyer et al. (2008)
Route
Dosing regimen
Animals/group at start
Group 1: Controls
Group 2: DMBA (10 mg/kg bw, p.o.)/
DMBAa
Group 3: MNU (50 mg/kg bw, i.p.)/
DMBAa
Group 4: E2, 3.0 mg, pellet implant/
DMBAa
8; 6 controls/group
3 and 6 mo groups
AIN-93M diet for 2 wk; then silastic
implant of E2 (0 or 27 mg over 24 wk)
Incidence of tumours
Mammary carcinoma
multiplicity at 3 and 6 mo,
respectively:
0; 0
0; 1.00 ± 0.78
0.67 ± 0.21; 0.80 ± 0.20
2.40 ± 0.68; 3.50 ± 0.50
Ovarian carcinoma
multiplicity at 3 and 6 mo,
respectively:
0.83 ± 0.48; 0.75 ± 0.11
3.58 ± 0.69; 4.40 ± 1.20
3.42 ± 0.49; 4.00 ± 0.82
7.40 ± 0.25; 9.50 ± 0.88
Mammary carcinomas
100% in all E2-treated
animals at 24 wk
Rat, ACI, BN, (BN x ACI)F1
(F1), and (BN x ACI)F2 (F2)
(F)
Schaffer et al. (2006)
E2: 27.5 mg, implanted
ACI: 23 rats
BN: 13 rats
F1: 22 rats
F2: 257 rats
Comments
Age at start NR;
weight, 50–55 g
NS; NS
NS; P < 0.05
P < 0.05; P < 0.05
P < 0.05a; P < 0.05a
–; –
P < 0.05; P < 0.05
P < 0.05; P < 0.05
P < 0.05b; P < 0.05b
Reduction of tumour volume;
reduction of tumour multiplicity
Control incidence not
specified but assumed
to be 0%
–; –
P < 0.0001; NS
P < 0.003; NS
P < 0.001; P < 0.027
Mammary carcinomas
(animals at risk):
Significance relative to ACI
strain
94%
0%
86%
58%
–
–
P < 0.05
P < 0.05
235
Estrogen-only menopausal therapy
Group 1: diet
Group 2: diet + 2.5% powdered
blueberry
Group 3: diet + 2.5% black raspberry
Group 4: diet + 400 ppm ellagic acid;
24 wk
19–25; 6 controls/group
Significance
Species, strain (sex)
Reference
Rat, Sprague Dawley (F)
Callejo et al. (2005)
Route
Dosing regimen
Animals/group at start
Single dose of DMBA 20 mg, dissolved
in 0.5 to 1 mL corn oil; estradiol
valerate, one daily dose, 5 mg/kg bw
i.m. starting at 11 wk
Group 1: control lpt + DMBA
Group 2: lpt + ovariectomy + DMBA
Group 3: lpt + ovariectomy + DMBA +
tibolone
Group 4: lpt + ovariectomy + DMBA +
raloxifene
Group 5: lpt + ovariectomy + DMBA
+ E2
10 animals/group
Rat, Sprague Dawley (F)
Kang et al. (2004)
Incidence of tumours
Significance
Mammary carcinomas
(mean tumours/group):
Differences with controls
4
0.1
0.3
–
P < 0.001
P < 0.001
0.1
P < 0.001
0.1
P < 0.001
Mammary carcinomas
(incidence; multiplicity):
DMBA, 10 mg in sesame oil; MNU,
50 mg/kg bw in saline; E3B 30 or
300 µg, implanted
DMBA alone
DMBA + E3B 30
DMBA + E3B 300
MNU alone
MNU + E3B 30
MNU + E3B 300
16 animals/group
4 animals/group killed at 5 wk
12 animals/group killed at 21 wk
11/12 (92%); 4.17 ± 0.96
6/12 (50.0%); 3.08 ± 1.17
8/12 (67%); 2.5 ± 1.52
7/12 (58%); 1.67 ± 0.57
4/12 (33%); 0.58 ± 0.30
7/12 (58%); 1.17 ± 0.46
Comments
E3B tends to decrease
the multiplicity of
DMBA or MNUinduced mammary
gland tumours
–; –
P < 0.05; NS
NS; NS
–; –
NS; NS
NS; NS
in the ovary
differs significantly from Groups 1 and 3
bw, bodyweight; d, day or days; F, female; DMBA, 7,12-dimethylbenz[a]anthracene; E2, 17β-estradiol; E3B, estradiol-3-benzoate; i.m., intramuscular; lpt, laparotomy; MNU: N-methylN-nitrosourea; mo, month or months; NR, not reported; NS, not significant; wk, week or weeks
a
b
IARC MONOGRAPHS – 100A
236
Table 3.1 (continued)
Estrogen-only menopausal therapy
of 20 mg of DMBA in pre-pubertal SpragueDawley rats randomized into five groups: Group
1 (control); Group 2 (castrated pre-pubertal
animals); and Groups 3, 4, and 5 (castration of
pre-pubertal animals followed by hormonal
treatment starting at puberty [11 weeks] with
tibolone, raloxifene, and estradiol, respectively).
For Group 5 (estradiol valerate), a single daily
dose of 5 mg/kg from a suspension of 1.5 mg/mL
was administered orally. Absence of ovarian
activity was observed in Groups 2, 3, 4, and 5,
as well as the expected variations in hormone
levels in all groups. Breast cancers were induced
in 100% of the animals in the control group, with
an average of four (2–7) tumours per animal in
this group. Only one cancer appeared in Groups
2, 3, and 4, and none appeared in Group 5.
Kang et al. (2004) used the DMBA and
MNU mammary carcinogenesis models to
evaluate the effects of estradiol-3-benzoate. The
hormone decreased the multiplicity of DMBA- or
MNU-induced mammary gland tumours. There
was also increased branching of the mammary
gland, and a decrease of estrogen receptor-α
(ERα) and estrogen receptor-β (ERβ). The inhibitory effect on mammary carcinogenesis may be
associated with the differentiation of mammary
gland and modulation of ERα and ERβ.
3.2.3Metabolites
Possible cancer suppressor effects of the
physiological metabolite of estradiol, 2-methoxyestradiol were evaluated by Cicek et al. (2007)
using a murine metastatic breast cancer cell
line injected to BALB/C mice. They found that
2-methoxyestradiol inhibited tumour growth
in soft tissue, metastasis to bone, osteolysis,
and tumour growth in bone. Tumour-induced
osteolysis was also significantly reduced in mice
receiving 2-methoxyestradiol.
3.3Synthesis
Estradiol causes malignant mammary
tumours in mice and malignant kidney tumours
in hamsters. Estrone causes malignant mammary
tumours in mice.
4. Other Relevant Data
4.1Absorption, distribution,
metabolism, and excretion
The absorption, distribution, metabolism
and excretion of estrogens have been extensively
reviewed previously in the IARC Monograph on
combined estrogen-progestogen menopausal
therapy (IARC 1999, 2007). In summary, cytochrome P450 1A1 and 1B1 catalyse the production of catechol estrogens that are further
oxidized to estrogen o-quinones that can induce
the formation of DNA damage. This is counteracted by the detoxification enzymes, catechol-Omethyltransferase, sulfotransferase, and uridine
5′-diphosphate(UDP)-glucuronosyl transferase
which reduce the levels of catechols by forming
methoxyestrogens, sulfates, and glucuronide
conjugates, respectively (IARC 1999, 2007). As far
as detoxification of the o-quinones are concerned,
there have been some reports that the quinones
can be detoxified through reduction by quinone
reductase and/or conjugation with glutathione
(GSH) catalysed by glutathione S-transferases
(GSTs) (Hachey et al., 2003; Zahid et al., 2008),
although the non-enzymatic reduction by nicotinamide adenine dinucleotide (phosphate)
(NAD(P)H) and Michael addition with GSH are
very facile reactions, enhanced enzymatic catalysis may be of questionable importance. A large
body of epidemiological data has failed to identify a consistent association between exposure to
estrogenic hormones and risk for cancer with any
single enzyme variant of these phase I and phase
II enzymes (Saintot et al., 2003; Boyapati et al.,
237
IARC MONOGRAPHS – 100A
2005; Cheng et al., 2005; Rebbeck et al., 2006;
Hirata et al., 2008; Justenhoven et al., 2008; Van
Emburgh et al., 2008), but possible interactions
between these genes remain to be examined in
more detail.
4.2Genetic and related effects
The genetic effects of endogenous estrogens, estradiol, and equine estrogens have been
reviewed previously (IARC, 1999, 2007). New
data that have appeared since are summarized
below.
4.2.1 Direct genotoxicity
(a) DNA adducts
Estrogen quinoids can directly damage
cellular DNA (see diethylstilbestrol, this volume;
Liehr, 2000; Bolton et al., 2004; Russo & Russo,
2004; Prokai-Tatrai & Prokai, 2005; Cavalieri
et al., 2006; IARC, 2007; Bolton & Thatcher,
2008; Gaikwad et al., 2008). The major DNA
adducts produced from 4-hydroxyoestradiolo-quinone are depurinating N7-guanine and
N3-adenine adducts resulting from 1,4-Michael
addition both in vitro and in vivo (Stack et al.,
1996; Cavalieri et al., 2000, 2006; Li et al., 2004;
Zahid et al., 2006; Saeed et al., 2007; Gaikwad
et al., 2008). Interestingly, only the N3-adenine
adduct may induce mutations because this
adduct depurinates extremely rapidly, whereas
the half-life of the N7-guanine adduct is
6–7 hours (Saeed et al., 2005; Zahid et al., 2006).
In contrast, the considerably more rapid isomerization of the 2-hydroxyestradiol-o-quinone to
the corresponding quinone methides results in
1,6-Michael addition products with the exocyclic amino groups of adenine and guanine
(Stack et al., 1996; Debrauwer et al., 2003). In
contrast to the N3- and N7-purine DNA adducts,
these adducts are stable which may affect their
repair and mutagenicity in vivo. A depurinating
N3-adenine adduct of 2-hydroxyestradiol quinone
238
methide has recently been reported in reactions
with adenine and DNA (Zahid et al., 2006). The
levels of this adduct in DNA were considerably
lower than corresponding depurinating adducts
observed in similar experiments with 4-hydroxyestradiol-o-quinone. This is consistent with the
suggestion that 2-hydroxylation does not lead
to cancer, whereas 4-hydroxylation results in
carcinogenesis. This same study (Zahid et al.,
2006) provided evidence to suggest that depurinating DNA adducts of estrogen quinoids were
formed in much greater abundance than stable
adducts. [The Working Group noted that this
implies a causal role for the depurinating adducts
in estrogen carcinogenesis; but these adducts
were analysed by methods (high-perfomance
liquid chromatography with electrochemical
detection) that differed from those used to detect
the stable adducts (32P-postlabelling/thin-layer
chromatography), making direct quantitative
comparisons somewhat problematic.]
It is important to mention that stable DNA
adducts at extracyclic aminogroups have been
detected by 32P-postlabelling in DNA from
Syrian hamster embryo cells treated with estradiol and its catechol metabolites. The rank
order of DNA adduct formation was 4-hydroxyestradiol > 2-hydroxyestradiol > estradiol. The
adduct formation correlated with cellular transformation (Hayashi et al., 1996). [The Working
Group noted that these data do not clarify the
relative importance of depurinating adducts
versus stable DNA adducts in catechol estrogen
carcinogenesis.]
For the major equine estrogens (equilin,
equilenin, and 17β-ol derivatives) the data
strongly suggests that the majority of DNA
damage also results from reactions of 4-hydroxyequilenin-o-quinone through a combination of
oxidative damage (ie. single-strand cleavage and
oxidation of DNA bases) and through generation of apurinic sites as well as stable bulky
cyclic adducts (Bolton & Thatcher, 2008). For
example, a depurinating guanine adduct was
Estrogen-only menopausal therapy
detected in in-vivo experiments with rats treated
with 4-hydroxyequilenin, following liquid
chromatography-tandem mass spectrometry
(LC/MS-MS) analysis of extracted mammary
tissue (Zhang et al., 2001). However, analysis of
this rat mammary tissue DNA by LC/MS-MS
also showed the formation of stable cyclic deoxyguanosine and deoxyadenosine adducts as well
as the aforementioned oxidized bases. Singlestrand breaks were also detected (Ding et al.,
2003; Kolbanovskiy et al., 2005; Yasui et al.,
2006; Ding et al., 2007). [The Working Group
noted that, interestingly, the ratio of the diasteriomeric adducts detected in vivo differs from
in-vitro experiments. This suggests differential
repair of these stereoisomeric lesions.] Using
highly sensitive nano LC/MS-MS techniques to
analyse DNA in five human breast tumours and
five adjacent tissue samples, including samples
from donors with a known history of Premarinbased hormone replacement therapy, cyclic
4-hydroxyequilenin-dC, -dG, and -dA stable
adducts were detected for the first time in 4/10
samples (Embrechts et al., 2003). [The Working
Group noted that although the sample size in this
study was small, and the history of the patients
is not fully known, these results suggest that the
equilin metabolite 4-hydroxyequilenin has the
potential to form a variety of DNA lesions in
humans.]
(b) Oxidative damage to DNA
As indicated earlier, these estrogens are
oxidized to o-quinones which are electrophiles
as well as potent redox active compounds (Bolton
et al., 2000). They can undergo redox cycling
with the semiquinone radical generating superoxide radicals mediated through cytochrome
P450/P450 reductase (Bolton et al., 2000; IARC,
2007; see diethylstilbestrol, this volume) which
gives rise to hydroxyl radicals. In support of this
mechanism, various free radical effects have
been reported in animals treated with estradiol
(IARC, 2007), including DNA single-strand
breaks (Nutter et al., 1991; Roy & Liehr, 1999),
8-hydroxydeoxyguanosine formation (Cavalieri
et al., 2000; Lavigne et al., 2001; Rajapakse et al.,
2005), and chromosomal abnormalities (Li et al.,
1993; Banerjee et al., 1994; Russo & Russo, 2006).
The estradiol catechol metabolite 4-hydroxyestradiol also induces oxidative stress and apoptosis
in human mammary epithelial cells (MCF-10A)
(Chen et al., 2005). [The high concentrations used
in this study (> 10 µM) have questionable physiological relevance.] It has been further shown
that the equilenin catechol, 4-hydroxyequilenin,
is also capable of causing DNA single-strand
breaks and oxidative damage to DNA bases both
in vitro and in vivo (IARC, 2007; Okamoto et al.,
2008). These and older data provide evidence
for the generation of reactive oxygen species by
redox cycling of estrogen metabolites – reactive
oxygen species that are known to damage DNA.
This is a proposed mechanism of estrogeninduced tumour initiation/promotion (Cavalieri
et al., 2000; Bolton & Thatcher, 2008).
(c) Genetic effects in women
Two studies have identified catechol estrogen
adducts in breast tissue of women with breast
cancer (see IARC, 2007), and the excessive
production of reactive oxygen species in breast
cancer tissue has been linked to metastasis in
women with breast cancer (Malins et al., 1996,
2006; Karihtala & Soini, 2007). [However, the
Working Group was not aware of studies on
markers of oxidative stress in women on estrogen
therapy.]
(d) Genetic effects in animals
There is some in-vivo evidence for estradiol
inducing DNA strand breaks, sister chromatid
exchange, chromosomal aberrations, and aneuploidy, but not micronuclei or covalent binding
of estrogen metabolites to DNA (IARC, 1999,
2007).
Injection of 4-hydroxyequilenin into the
mammary fat pads of Sprague-Dawley rats
239
IARC MONOGRAPHS – 100A
resulted in a dose-dependent increase in singlestrand breaks and oxidized bases as analysed
by the comet assay, and the formation of
8-hydroxydeoxyguanosine and 8-hydroxydeoxyadenine (Zhang et al., 2001). In mice treated
with equilenin, the levels of 8-hydroxydeoxyguanosine were increased 1.5-fold in the uterus
(Okamoto et al., 2008).
not consistently been observed (IARC, 1999,
2007). The mutagenic properties of the aforementioned stable DNA adducts derived from
2-hydroxyestrogen-quinone-methide have been
evaluated using oligonucleotides containing sitespecific adducts transfected into simian kidney
(COS-7) cells where G→T and A→T mutations
were observed (Terashima et al., 2001).
(e) Genetic effects in human and animal cells
4.2.2Indirect effects related to genotoxicity
There is some evidence for estradiol inducing
DNA strand breaks, sister chromatid exchange,
and chromosomal aberrations in various human
cells, including MCF-7 breast cancer cells,
although the evidence for induction of aneuploidy in human cells is equivocal (IARC, 1999,
2007).
Repeated treatment at physiological (70 nM)
and at much lower (0.007 nM) doses of estradiol
of MCF-10F immortalized human breast epithelial cells, which are ERα-negative, increased
colony formation in a soft agar assay (Russo
et al., 2001, 2003). When grown in collagen,
these cells changed from differentiated ductular
growth to solid-spherical masses with the same
dose–response relationship, and invasive growth
in a Matrigel assay was increased (Russo et al.,
2002, 2006). Following estradiol exposure at a
concentration of 70 nM of MCF-10F cells for four
alternating 24-hour periods, several passages of
the cells and subsequent selection, four clones
grew in Matrigel, two of which formed tumours
in nude mice (Russo et al., 2006). Both clones
had loss of chromosomal region 9p11–3 and all
other subclones had variable other chromosomal
losses, deletions, and gains. [The Working Group
noted that this study established that estradiol is
capable of inducing malignant transformation in
cultured immortalized human breast cells that
are ER-negative.]
The same types of genetic damage induced in
vivo are also induced in cells in culture by estradiol, estrone, and their catechol metabolites as
well as cell transformation, but mutations have
240
(a) Estrogen-receptor-mediated effects
Receptor-mediated mechanisms by which
estrogens may cause or contribute to carcinogenesis have previously been reviewed extensively
(IARC, 1999, 2007). Estrogen therapy in the
menopause increases the rate of cell proliferation
in the postmenopausal human breast (IARC,
1999, 2007). This effect is mediated through
nuclear ER-mediated signalling pathways, and
this results in an increased risk of genomic
mutations during DNA replication (Nandi et al.,
1995; Feigelson & Henderson, 1996; Henderson
& Feigelson, 2000; Flötotto et al., 2001; Yager &
Davidson, 2006). [The Working Group noted that
direct evidence for this mechanism in relevant
experimental models of target tissues is, however,
not available at present.] Similarly acting nongenomic pathways, potentially involving newly
discovered membrane-associated estrogen
receptors, appear to regulate extranuclear
estrogen signalling pathways that can affect
cell proliferation (Björnström & Sjöberg, 2005;
Revankar et al., 2005; Song et al., 2006; Yager &
Davidson, 2006; Hammes & Levin, 2007; Pietras
& Márquez-Garbán, 2007; Levin & Pietras, 2008).
Recent studies have shown the presence of ERα
and ERβ in the mitochondria of various cells and
tissues, which may be involved in deregulation
of mitochondrial bioenergetics, and conceivably
contribute to estrogen-exposure-related cancers
(Yager & Davidson, 2006; Chen et al., 2008).
Cross-talk between these genomic and nongenomic second-messenger pathways may have
Estrogen-only menopausal therapy
an important role in estrogenic control of cell
proliferation, inhibition of apoptosis, and induction of DNA damage (Yager & Davidson, 2006).
4.3Synthesis
Receptor-mediated responses to hormones
are a plausible and probably necessary mechanism for estrogen carcinogenesis. In addition,
there is support for a genotoxic effect of estrogenic hormones or their associated by-products
such as reactive oxygen species. The types of
DNA damage found in cells and tissues exposed
to estrogens are consistent with such genotoxic
effects. Current knowledge does not allow a
conclusion as to whether either of these mechanisms is the major determinant of estrogeninduced cancer. It is entirely possible that both
mechanisms contribute to and are necessary for
estrogen carcinogenesis. Although there appears
to be a direct link between exposure to estrogens,
metabolism of estrogens, and increased risk of
breast cancer, the factors that affect the formation, reactivity, and cellular targets of estrogen
quinoids remain to be fully explored.
5.Evaluation
There is sufficient evidence in humans for
the carcinogenicity of estrogen-only menopausal therapy. Estrogen-only menopausal
therapy causes cancer of the endometrium and
of the ovary. Also, a positive association has been
observed between exposure to estrogen-only
menopausal therapy and cancer of the breast.
For cancer of the colorectum, there is evidence
suggesting lack of carcinogenicity. An inverse relationship has been established between exposure
to estrogen-only menopausal therapy and cancer
of the colorectum.
There is sufficient evidence in experimental
animals for the carcinogenicity of some estrogens used in estrogen-only menopausal therapy.
Estrogen-only menopausal therapy is carcinogenic to humans (Group 1).
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